The instrumented correction of spinal deformity, and particularly scoliosis, using an anterior approach has been proven to be a successful technical concept. Clinical and scientific work has shown it to be an ideal technique for treating the majority of idiopathic scoliosis types.
In comparison to posterior scoliosis surgery, the use of very early anterior derotation and fusion for selective treatment of thoracic and thoracolumbar curves was shown to save up to two fusion levels compared to the posterior approach. Further, the anterior approach does not disrupt the posterior muscles, it is better at restoring sagittal profile of the spine, it enables real derotation through an anterior column release and direct vertebral manipulation close to the centre of rotation.
As noted above, the use of modern instruments to provide an anterior scoliosis fixation provides significant advantages. A known approach is the use of an instrument with two rods. The use of such a double rod system improves the ease of reconstructing and maintaining a physiologic sagittal spino-pelvic alignment. An exemplary two rod system is described in U.S. Pat. No. 5,702,395. This document describes a spinal osteosynthesis instrumentation for an anterior approach. The instrumentation comprises two rigid rods parallel to each other, and at least two blocks adapted to transversely interconnect the rods, as well as bone anchorage elements for the blocks. The two blocks and the two associated rods make a rectangular frame, which is said to afford all of the required stability for restoring the axial continuity of the vertebral column, avoids correction losses, and facilitates the consolidation of the bone graft.
Recent developments in implant technology have increased the biomechanical stabilisation potential of anterior constructs. Hence, the number of pathologies that can be managed with anterior-only strategies has rapidly increased.
However, with both anterior-only scoliosis correction and reconstruction of the anterior column in other deformities, the amount of corrective force applied to the instrumentation is limited by the interface strength and pull out resistance of the screws anchoring the instrument to the vertebral body. Hence, further development of implants and screws used for anterior spinal surgery has the potential to increase construct stability, broaden the indications for which anterior column surgery is suitable and push the limits of current techniques and corrections that are currently achieved.